System and Method for Enabling a Dual-Wire Protocol

ABSTRACT

A system and method for enabling a dual-wire protocol (DWP). A low-power alternative to the single wire protocol (SWP) is provided that uses an extra wire. DWP can reduce the NFC chip&#39;s current requirement to almost zero, while enabling higher transmission rates.

This application claims the benefit of and priority to provisionalapplication No. 61/986,203, filed Apr. 30, 2014, which is incorporatedherein by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates generally to digital communications and,more particularly, to a system and method for enabling a dual-wireprotocol.

2. Introduction

Near field communication (NFC) is a set of standards for mobile devicesthat establish close-proximity wireless communication. It is anticipatedthat NFC will enable various mobile applications including contactlesstransactions, data exchange, and simplified setup of more complexcommunications. NFC can also be used between an NFC device and anunpowered NFC chip.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features can be obtained, a more particular descriptionwill be rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments and are not therefore to be consideredlimiting of its scope, the disclosure describes and explains withadditional specificity and detail through the use of the accompanyingdrawings in which:

FIG. 1 illustrates an example embodiment of an NFC system.

FIG. 2 illustrates and example embodiment of communication between anNFC controller chip and a secure element chip.

FIG. 3 illustrates a flowchart of an example process.

DETAILED DESCRIPTION

Various embodiments are discussed in detail below. While specificimplementations are discussed, it should be understood that this is donefor illustration purposes only. A person skilled in the relevant artwill recognize that other components and configurations may be usedwithout parting from the spirit and scope of the present disclosure.

The Single Wire Protocol (SWP) is an existing specification for asingle-wire connection between a Secure Element (SE) chip and an NFCchip. In one example, the NFC chip and the SE chip are included in amobile device (e.g., mobile phone).

In SWP, the NFC chip is configured to transmit information onto the wireby driving voltages 0 V and 1.8V, while the SE chip transmitsinformation onto the wire by sinking 0 mA or 1 mA current, wheneverthere is 1.8V on the wire. Unfortunately, 1 mA is a significant portionof the NFC chip's current budget in low-power mode. In addition, SWPtransmission rates are limited to only 1.7 Mbps.

As will be described in greater detail below, a low-power alternative toSWP is provided that uses an extra wire. This extra wire produces atwo-wire protocol that is referred to herein as a Dual Wire Protocol(DWP). At the expense of one extra wire, DWP can reduce the NFC chip'scurrent requirement to almost zero, while enabling higher transmissionrates (e.g., quadruple or higher) as compared to SWP.

In one embodiment, a DWP device is provided that incorporates a firstphysical layer device (PHY) that is configured to communicatebi-directionally with a second PHY via SWP. As noted, communication in afirst direction over the single wire using SWP is via a voltage signalwhile communication in a second direction over the single wire using SWPis via a current signal. The DWP device also includes a digitalcommunication block that is configured to transmit and to receivecommunication signals. When operating in an SWP mode, the digitalcommunication block would transmit and receive over the single wire viathe PHY.

To facilitate the selective operation in either the SWP or DWP modes,the DWP device includes a selector module that is configured to couplethe first PHY to an interface pin of the DWP device when the DWP deviceoperates in the SWP mode for detection by the first PHY of a currentsignal from a second device, and to couple the digital communicationblock to the interface pin of the DWP device when the device operates ina DWP mode for detection by the digital communication block of a voltagesignal from the second device.

In one embodiment, a process of a DWP device is provided, which includesdetermining, by a DWP device, whether to communicate with a seconddevice using either SWP where communication in a first direction over asingle wire is via a voltage signal and communication in a seconddirection over the single wire is via a current signal or DWP wherecommunication over two wires is via voltage signals. Based on thedetermined communication mode, the process would then proceed toconfigure a selector module within the DWP device based on thedetermination. In one embodiment, the selector module is configured tocouple a PHY to an interface pin of the DWP device when the deviceoperates using SWP for detection by the PHY of a current signal from asecond device, and is configured to couple the digital communicationblock to the interface pin of the DWP device when the DWP deviceoperates using DWP for detection by the digital communication block of avoltage signal from the second device.

Prior to describing the details of a configurable DWP device that canselectively operate in an SWP or a DWP mode, reference is made first toFIG. 1, which illustrates an example embodiment of an NFC system. Asillustrated, the NFC system includes mobile device 110 and NFC device120 (e.g., a reader device). In this high-level illustration, mobiledevice 110 further includes NFC element 112 and SE 114. Communicationbetween NFC element 112 and SE 114 can be enabled using SWP or DWP,depending on the particular communication protocols supported by NFCelement 112 and SE 114.

In general, an SE chip can represent a tamper-resistant chip thatfacilitates the secure storage of confidential information. For example,an SE chip can be configured to store confidential payment informationand other sensitive credential information. SE chips can be applied tovarious applications, and can be embodied in various form factors (e.g.,SmartCard, UICC(SIM), eSE, micro SD, or any other secure storageelement).

In general, an SE chip can represent a computing environment on a singlechip, complete with a secure microcontroller, ROM, EEPROM, RAM and I/Oport. The SE chip can also include a cryptographic co-processor that isconfigured to implement common algorithms such as DES, AES and RSA. SEchips are certified for tamper-resistant use, making it difficult toextract data by disassembling or analyzing the SE chip. SE chips canalso be pre-programmed with a multi-application OS that takes advantageof the hardware's memory protection features to ensure that eachapplication's data is only available to itself. Application installationand (optionally) access is controlled by requiring the use ofcryptographic keys for each operation.

Here, it should be noted that the extensive qualification andcertification process required of SE chips can lead to significantdelays in the adoption of new communication protocols by particular SEchips. As such, the pace at which next-generation technologies areadopted by the SE chips relative to NFC chips will differ substantially.It is recognized by the present disclosure that the adoption of anext-generation DWP by NFC chips can be in tandem with backwardscompatibility with SE chips that only support previous-generation SWPtechnology.

FIG. 2 illustrates an example embodiment of communication between NFCchip 210 and SE chip 220, both of which can be configured to operate ineither an SWP or a DWP mode. In facilitating support for SWP and DWPmodes, both NFC chip 210 and SE chip 220 can be based on encode/decodehardware that is already used for the existing SWP. This encode/decodehardware is illustrated as SWP PHY 214 in NFCC chip 210 and SWP PHY 222in SE chip 220.

As would be appreciated, SWP PHY 212 in NFC chip 210 can be configuredto drive voltages of 0V and 1.8V when transmitting, while also includinga current sensor that would enable SWP PHY 212 to detect when SE chip220 is sinking 1 mA current on the single wire. Similarly, SWP PHY 222in SE chip 220 can include resistors and transistors that are connectedin a series/parallel configuration that can be configured to drawcurrent on the single wire when 1.8V is present on the single wire. Thenumber of transistors turned on can be changed to adjust the resistanceand current draw of the circuit. As would be appreciated, the particularimplementation details of SWP PHY 212 in NFC chip 210 and SWP PHY 222 inSE chip 220 in supporting SWP would not limit the scope of the presentdisclosure.

Support for both the SWP and DWP modes can be enabled through one ormore selector modules (e.g., multiplexers) that configure NFC chip 210and SE chip 220. Consider first the configuration into the SWP mode. ForNFC chip 210, selector module 216 would be configured to couple SWP PHY212 in NFC chip 210 to interface pin 252, while selector module 217would couple SWP PHY 212 in NFC chip 210 to digital communication block214 of NFC chip 210. Selector module 215 in NFC chip 210 would notcouple digital communication block 214 to interface pin 251. Rather,digital communication block 214 would be coupled directly to SWP PHY212. Here, it should be noted that selector module 215 can also be usedto send other I/O mux signals to interface pin 251. For SE chip 220,selector module 226 would be configured to couple SWP PHY 222 in SE chip220 to interface pin 254, while selector module 225 would be configuredto couple SWP PHY 222 in SE chip 220 to digital communication block 224.

In this configuration, SWP PHY 212 in NFC chip 210 and SWP PHY 222 in SEchip 220 would be enabled to perform transmit encoding and receivedecoding on behalf of their respective digital communication blocks 214and 224, respectively. Communication between SWP PHY 212 in NFC chip 210and SWP PHY 222 in SE chip 220 would then be via SWP over a single wirethat connects interface pin 252 of NFC chip 210 to interface pin 254 ofSE chip 220. As would be appreciated, this configuration of NFC chip 210and SE chip 220 would represent the connectivity of an NFC chip and SEchip that only supported SWP.

For the DWP mode, the SE chip's transmit signal is a voltage rather thana current. Additionally, the signal is transmitted on a separate wire.Thus, there are now two wires that carry separate voltage transmitsignals. In the DWP mode, digital communication block 214 in NFC chip210 and digital communication block 224 in SE chip 220 would retain thesame base functionality. Since the SE chip is designed to transmitvoltage signals during the DWP mode, digital communication block 214 inNFC chip 210 can be connected directly to digital communication block224 in SE chip 220.

More specifically, for NFC chip 210, selector module 215 would beconfigured to couple digital communication block 214 to interface pin251, while selector module 216 and selector module 217 would beconfigured to couple digital communication block 214 to interface pin252. SWP PHY 212 would be de-coupled from interface pin 252. For SE chip220, selector module 225 would be configured to couple digitalcommunication block 224 to interface pin 253, while selector module 226would be configured to couple digital communication block 224 tointerface pin 254. SWP PHY 222 would be de-coupled from interface pin254.

In this DWP configuration, transmission from NFC chip 210 to SE chip 220would be based on a voltage signal on the first wire connectinginterface pin 251 of NFC chip 210 to interface pin 253 of SE chip 220,while transmission from SE chip 220 to NFC chip 210 would be based on avoltage signal on the second wire connecting interface pin 254 of SEchip 220 to interface pin 252 of NFC chip 210. As DWP is based ontransmission using voltage signals, faster transmission rates can beachieved using faster clocks driving existing SWP logic.

As noted, an SE chip may or may not support DWP. As such, the NFC chipmay not know whether the SE chip with which it is communicating is anSWP or DWP device. One of the features of the NFC chip is that it cansupport a detection procedure to identify the particular mode in whichit should operate. In one embodiment, the detection procedure iscontrolled by control element 230 in digital communication block 214.

In one embodiment, the detection procedure assumes that the NFC chip iscommunicating with an SWP device. When the NFC chip drives voltage ontothe SWP wire, the NFC chip uses it's own SWP PHY to listen for one oftwo current levels. For example, a first current level of 1 mA wouldindicate an SWP mode, while a second, lower current level (e.g., 0.25mA) would indicate a DWP mode.

Consider a scenario where the SWP PHY in the SE chip includes two seriesresistor/transistor sections in a parallel configuration, where a firstsection produces a resistor of value 3R, while the second sectionproduces a resistor of value 1R. With this proportion of resistorvalues, the SE chip can be configured to turn on both sections or onlythe first section. To signal a DWP mode, both sections can be turned on,such that the equivalent resistance of both fingers is 0.75R. To signala SWP mode, on the other hand, only the first section can be turned on,such that only the 3R resistance of the first section is presented. Asthe indication of the SWP mode presents four times as much resistance ascompared to the indication of the DWP mode, the current drawn would befour times as much in the indication of the SWP mode as compared to theindication of the DWP mode. Where the value of R is sized appropriately,the indication of the SWP mode can draw 1 mA, while the indication ofthe DWP mode can draw 0.25 mA.

Once NFC chip 210 has recognized the lower current level (e.g., 0.25mA), NFC chip 210 can begin transmitting via interface pin 251, ratherthan through SWP PHY 212. SE chip 220, listening on interface pin 253,would recognize a signal from NFC chip 210 and would switch selectormodule 225 to receive from interface pin 253 rather than SWP PHY 222.Conversely, SE chip 220 would switch selector module 226 to enable thetransmission of voltage signals directly onto interface pin 254, ratherthan through SWP PHY 222. NFC chip 210 would then switch selectormodules 216 and 217 to enable receiving of voltage signals on interfacepin 252, rather than via SWP PHY 212.

In another embodiment, the NFC chip can detect whether or not the SEchip is a DWP device through a dedicated input pin that indicates an SWPmode or a DWP mode. This dedicated input pin can be driven by the SEchip, statically driven high or low on the PCB board, or leftunconnected. If the dedicated input pin is left unconnected, a pullresistor internal to the NFC chip can be used to indicate the defaultselection.

Having described an embodiment of an NFC chip and SE chip that cansupport both SWP and DWP, reference is now made to FIG. 3, whichillustrates a flowchart of an example process. As illustrated, theprocess can begin at step 302 where a communication mode measurement isreceived. In various embodiments, the communication mode measurementwould enable the NFC chip and/or the SE chip to assess whichcommunication mode should be used. As noted above, various mechanismscan be used to derive a communication mode decision process. In general,the communication mode measurement can be part of an activeconfiguration process between the NFC chip and SE chip, can be based onpre-set input pin settings, can be based on pre-set register settings,or any other mechanism that enables the NFC chip and/or SE chip todetermine whether an SWP mode or DWP mode should be used. In general,the particular configuration mechanism used would be implementationdependent and would not limit the scope of the present disclosure.

After the communication mode measurement is completed, the process wouldthen continue to step 304 where a determination of a particularcommunication mode is made based on the communication mode measurement.In one embodiment, the determination can be controlled by a controlelement incorporated within a digital communication block within the NFCchip. As would be appreciated, the particular mechanism by which thedetermination is made would be dependent on the particular type ofcommunication mode measurement that is used as an input to thedetermination process.

Next, at step 308, the device is configured based on the determinedcommunication mode. As described in the example embodiment above, theconfiguration can include the configuration of one or more selectormodules (e.g., multiplexers) that are used to configure the connectivitywithin the device. This particular example mechanism of configuration isnot intended to be limiting. In general, any mechanism that enables achange in configuration to support a DWP mode relative to an SWP mode inthe device can be used.

As has been described, the present disclosure presents a device that canbe configured into either a DWP mode or an SWP mode. As the DWP modesupports voltage signaling on two separate wires, the DWP mode canprovide a low-power mode relative to the SWP mode. This low-power DWPmode can support higher transmission rates. Moreover, this low-powermode can be advantageous in supporting application scenarios where thedevice incorporating the NFC and SE is not actively powered.

While the above description has focused on a particular application ofDWP to communication between an SE and NFC, such an application is notintended to be limiting. DWP can be applied to communication betweenother chips that can benefit from two-wire voltage signaling.

Another embodiment of the present disclosure can provide a machineand/or computer readable storage and/or medium, having stored thereon, amachine code and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein.

Those of skill in the relevant art would appreciate that the variousillustrative blocks, modules, elements, components, and methodsdescribed herein may be implemented as electronic hardware, computersoftware, or combinations of both. To illustrate this interchangeabilityof hardware and software, various illustrative blocks, modules,elements, components, methods, and algorithms have been described abovegenerally in terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system. Thoseof skill in the relevant art can implement the described functionalityin varying ways for each particular application. Various components andblocks may be arranged differently (e.g., arranged in a different order,or partitioned in a different way) all without departing from the scopeof the subject technology.

These and other aspects of the present disclosure will become apparentto those skilled in the relevant art by a review of the precedingdetailed disclosure. Although a number of salient features of thepresent disclosure have been described above, the principles in thepresent disclosure are capable of other embodiments and of beingpracticed and carried out in various ways that would be apparent to oneof skill in the relevant art after reading the present disclosure,therefore the above disclosure should not be considered to be exclusiveof these other embodiments. Also, it is to be understood that thephraseology and terminology employed herein are for the purposes ofdescription and should not be regarded as limiting.

What is claimed is:
 1. A device, comprising: a first single wireprotocol physical layer device that is configured to communicatebi-directionally with a second single wire protocol physical layerdevice via a single wire, wherein communication in a first directionover the single wire is via a voltage signal and communication in asecond direction over the single wire is via a current signal; a digitalcommunication block that is configured to transmit and to receivecommunication signals; and a selector module that is configured tocouple the first single wire protocol physical layer device to aninterface pin of the device when the device operates in a first modeusing a single wire protocol for detection by the first single wireprotocol physical layer device of a current signal from a second device,and to couple the digital communication block to the interface pin ofthe device when the device operates in a second mode using a two wireprotocol for detection by the digital communication block of a voltagesignal from the second device.
 2. The device of claim 1, wherein theselector module is a multiplexer.
 3. The device of claim 1, wherein thesecond device is a Secure Element (SE) chip.
 4. The device of claim 1,wherein the digital communication block includes a control element thatis configured to determine whether to communicate in the first mode orthe second mode.
 5. The device of claim 4, wherein the control elementis responsive to an input pin that is used to indicate the first mode orthe second mode.
 6. The device of claim 4, wherein the control elementis responsive to an amount of current drawn by the second device.
 7. Amethod, comprising determining, by a digital communication block in afirst device, whether to communicate with a second device using either asingle wire protocol where communication in a first direction over asingle wire is via a voltage signal and communication in a seconddirection over the single wire is via a current signal or a two wireprotocol where communication over two wires is via voltage signals; andconfiguring a selector module within the first device based on thedetermination, wherein the selector module is configured to couple asingle wire protocol physical layer device to an interface pin of thefirst device when the first device operates using the single wireprotocol for communication by the single wire protocol physical layerdevice with a second device via a current signal, and the selectormodule is configured to couple the digital communication block to theinterface pin of the first device when the first device operates usingthe two wire protocol for communication by the digital communicationblock with the second device via a voltage signal.
 8. The method ofclaim 7, wherein the selector module is a multiplexer.
 9. The method ofclaim 7, wherein the second device is a Secure Element (SE) chip. 10.The method of claim 7, wherein the second device is a Near FieldCommunication (NFC) chip.
 11. The method of claim 7, wherein thedetermining comprises determining using an input pin that indicates thefirst mode or the second mode.
 12. The method of claim 7, wherein thedetermining comprises determining using an amount of current drawn bythe second device.
 13. A secure element device, comprising: a firstsingle wire protocol physical layer device that is configured tocommunicate bi-directionally with a second single wire protocol physicallayer device via a single wire, wherein communication in a firstdirection over the single wire is via a voltage signal and communicationin a second direction over the single wire is via a current signal; adigital communication block that is configured to transmit and toreceive communication signals; and a selector module that is configuredto couple the first single wire protocol physical layer device to aninterface pin of the secure element device when the device operates in afirst mode using a single wire protocol for transmission of a currentsignal to a second device, and to couple the digital communication blockto the interface pin of the secure element device when the deviceoperates in a second mode using a two wire protocol for transmission bythe digital communication block of a voltage signal to the seconddevice.
 14. The secure element device of claim 13, wherein the selectormodule is a multiplexer.
 15. The secure element device of claim 13,further comprising a second selector module that is configured to couplethe digital communication block to a second interface pin of the devicewhen the device operates in the second mode for receipt of a voltagesignal from a second device, and to couple the digital communicationblock to the first single wire protocol physical layer device when thedevice operates in the second mode for receipt by the digitalcommunication block of a voltage signal from the first single wireprotocol physical layer device.
 16. The secure element device of claim13, wherein the first single wire protocol physical layer device isconfigured to communicate two different non-zero current signal levelsto the second device, wherein one of the two different non-zero signallevels communicates whether the secure element device supports thesecond mode.